1. Field of the Invention
The present invention relates to an X-ray CT scanner and, particularly, it relates to an X-ray CT scanner and an image-data generating method capable of efficiently generating image data in a desired image section.
2. Description of the Related Art
High-speed and high-performance X-ray detectors and processors have allowed recent X-ray CT scanners to display CT images in slice planes (sections orthogonal to the body axis of a subject) in real time owing to a high-speed image reconstruction which is executed in parallel with acquisition of X-ray projection data.
Furthermore, the use of two-dimensional X-ray detector in which multiple X-ray detecting elements are disposed not only in a scanning direction (the rotating direction of the frame) but also in a slice direction (in the direction of the body axis of a subject) allows practical application of multislice CT scanners capable of acquiring X-ray projection data (hereinafter, referred to as projection data) in multiple slice planes and generating image data in the slice planes (axial image data) substantially at the same time.
On the other hand, in order to obtain image data in a desired section other than the axial image data, the diagnostic region of the subject is shifted along the body axis to generate multiple axial image data or three-dimensional volume data by using acquired projection data, from which image data (what is called multi-planar reconstruction (MPR) image data) in the desired image section is generated. (For example, refer to JP-A-2003-116838, pp. 11-12, FIGS. 9-10)
It is not easy to grasp three-dimensional information in the diagnostic region of a subject from multiple axial image data. Accordingly, MPR image data in an optimum section for the diagnostic region has conventionally been generated on the basis of the axial image data, as has been described above. In that case, multiple axial image data in the diagnostic region must be combined first to generate three-dimensional image data. This requires much time to generate the three-dimensional image data, making it difficult to generate MPR image data in a short time, which results in not only decreasing diagnostic efficiency but also placing a heavy load on the operator.
On the other hand, decreasing the number of pixels of the axial image data or increasing slicing distance can decrease the time required to generate three-dimensional image data. However, also the pixels of MPR image data generated from the acquired three-dimensional image data are roughened and so low-resolution MPR image data is generated. Briefly, the resolution of an image and image-data generation time are in trade-off relationship, which were not satisfied at the same time.